Method of treating well bore walls



A TTOR/VE YS June 12, 1951 J. o. cRoucH ETAL METHOD 0F TREATING WELL BORE WALLS Filed )lay 8, 1946 Patented June 12, 195,1

METHOD 0F TREATING WELL BORE WALLS James 0. Crouch, Kilgore, Tex., and Orln W. Lyons, Shreveport, La., assignors to The Dow Chemical Company, a corporation of Delaware Application May 8, 1946, Serial No. 668,078

1 Claim. 1 The invention relates to methods of treating the bore wall of deep wells, especially those drilled for oil or gas. It more particularly concerns the treatment of a bore Wall so as to seal those portions which would otherwiseI deliver an unwanted fluid or sloughings into the well from the surrounding formation.

In the usual practice of constructing deep wells, the portion of the well bore overlying the productive formation is cased Wtih steel pipe While the portion penetrating the productive stratum is oftentimes uncased. Fluids from the uncased portion may enter the well and be withdrawn as by pumping or flowing the well. Such well construction has several disadvantages among which are` that no means are provided for controlling.v

the entry into the uncased portion of the well of -either an'unwanted fluid or earth particles.

Recently, attempts have been made to overcome the foregoing disadvantages by impregnating Such method, when it can be used, has the advantage of simplicity and ease of execution, and it is effective not only to control sloughing but also to exclude uids except from the zones selected for perforation. The resinforming liquids used for the purpose are mobile liquids when first compounded and spontaneously undergo polymerization or condensation or chemical reaction so that they gradually thicken and harden in time into a solid resin, the rate of hardening increasing with the temperature and amount of catalyst used, if any, to promote the hardening reaction. A number of examples of resin-forming liquids suitable for the purpose are set forth in U. S. Patent No. 2,274,297, those of the phenol-aldehyde type being generally preferred although other resin-forming liquids may' be used.

Among the disadvantages of the method arethat the depth of impregnation varies with the pressure applied to the sealing liquid and with the permeability of the earth formations undergoing treatment, being greater the greater the applied pressure and permeability. As a result in Well bores traversing formations having different permeabilities in different portions, at a given impregnation pressure sufficient to properly impregnate the less permeable portions so that they may be perforated at desired points, the more permethey may be successfully perforated, the less permoderate thickness throughout its extent.

meable portions are under impregnated so that an imperfect barrier to unwanted fluids and sloughings is had.

Attempts to control the variation in penetration of the sealing liquid into the formation, due to variations in its permeability, by the conventional expedient of adding to the sealing liquid a filler, such as shredded or powdered asbestos, hemp, saw dust, wood fiber, or the like, are not successful. The penetration is too great and irregular in spite of the use of conventional fillers, varying as without the filler, with the variations in permeability of the earth, to permit success-4 ful perforation of the impregnated bore Wall at the desired points.

One of the objects of the invention is to provide a method of treating the bore wall with a fluid sealing agent capable of setting in situ so that the depth of penetration is controlled and limited to a predetermined amount and rendered substantially independent of variations in permeability of the formations surrounding the well bore. A particular object is to provide a method of forming of the outer layer of the well bore wall a sealed perforatable sheath of uniform thickness so that all portions may be perforated with equivalent facility. Still other objects and advantages will become apparent as the description of the invention proceeds. Y

We have discovered that by including in the resin-forming liquid a filler of comminuted solids inert to the resin-forming liquid and graded as to particle size so that the filler. comprises particles all below about 1000 microns in size (i. e, diameter or greatest dimension) and including a substantial proportion of very small size, hereinafter set forth, the depth of penetration of the resin-forming liquid into the earth formation is thereby limited in proportion to the amount of the filler added and is not substantially affected by variations in permeability of the earth formation. By means of a suitable amount of such filler, we are enabled to control the depth of impregation of a well bore wall with a resin-forming liquid to about 0.5 to 6 inches so as to obtain a fluid-tight sheath of substantially uniform and The uniform and moderate thickness of the sheath then permits it to be perforated at any desired point Without failure. By this method, a well making practice is provided that permits passages from the earth formation to the well bore to be made at any point in the well bore wall, as by gun perforation, while a completely sealed vwell bore wall is obtained atall other points,

thereby preventing undesired fluids and sloughings from entering the well.

As regards the filler, we have found that to be effective it must contain particles which are fairly uniformly graded as to size froma maximum.

size of 1000 microns to a minimum size of about 0.006 micron. A proper distribution of the filler particle sizes over the gradient of 1000 microns to 0.006 and the respective amounts of each size in each range in the gradient is as follows: About 25 to 40 per cent by weight of the filler mixture may contain particles in the range 1000 to 100 microns, about 25 to 40 per cent in the range 100 to 1 microns, about 12 to 20.per cent in the range 1 to 0.01, and about 12 to 20 percent in the range 0.01 to 0.006 micron'. Various combinations of nely divided materials may be used to produce :filler mixtures having the proper amounts of the proper size particles according to these specifications.` Mixtures of solid particles of the aforesaid ranges may be formed of a mixture of ground mica, e. g. 'biotite mica or other suitable mineral matter, such as silica, for the particles in the range 1000 to 100 microns; ground iron oxide (FezOa) o1' other suitable mineral matter for the particles in the range 100 to 1; a ground pigment, e. g. chrome yellow, chromium oxide, barium sulphate, China clay, magnesium silicate, or other suitable mineral matter for particles in the range 1 to 0.01; and an organic hydrophilic colloid, e. g.V a starch, casein, gelatine, gum gluten, agar agar, isoalgin, and devitalized gluten for the particles in the range 0.01 to 0.006.

As illustrative of the penetration control obtained, tests were made of the use of filler mir'- tures containing per 100 parts of mixture by weight 33.3 parts of biotite mica, having substantially all its particles in the range 1000 to. 100 microns; 33.3 parts of a clay, having substantially all its particles in the range 100 to 1 microns; 16.7 per cent of a clay, having substantially all its particles in the range 1 .to 0.01 micron; and 16,7 per cent of gum gluten, having substantially all its particles in the range 0.01 to 0.006 micron. In these tests, various amounts of the foregoing ller mixture were added to a phenol-aldehyde type resin-forming liquid containing an alkaline catalyst to promote condensation and hardening, the hardening being complete in about 4 hours. Each mixture was tested at 150 F. under a pressure of 2000 p. s. i. against unconsolidated Ottawa sand in a column about 12 inches long. The sand column had a permeability of 57 darcies and the pressure was maintained on the mixture of ller and resinforming liquid thereby tending to drive it into the sand column while the resin-forming liquid hardened.

The results obtained are set forth Yin Table I.

Temperature, 150 F., pressure applied 20 p. s. i.

Inches 6.0 0. 75 5. 5 1.25 5.0 l. 50 4. 5 1.75 4. 2.0 3. 2. 5 3. 0 3. 0

Thus with a given ller mixture containing substantial amounts of particles in each of the size classes aforementioned, one may control or regulate the depth to which the sealing liquid penetrates the well wall before hardening occurs, by suitably regulating the proportion of ller used. In the foregoing table, the data given show that the depth of penetration Varies inversely with the concentration of the ller in the sealing liquid for the same applied pressure.

Further tests have shown that the depth of penetration is not substantially aiected by the permeability of the earth formations so that the depth of impregnation by the resin-forming liquid of the earth formations is substantially independent of variations .in fluid permeability of their fluid permeable portions. Laboratory tests of the kind described also vprovide a substantially accurate gauge of the penetration to be expected into a uid permeable well wall at comparable temperatures and pressures regardless of variations in fluid permeability. The amount of nller to use, then, is based upon tests of the kind described and the depth of penetration desired. Y Greater or less depth of penetration may be had by altering the choice of finely divided filler solid in each of the respective size classes. For example, by substituting casein for gum gluten given in the foregoing exampleand using 6 pounds of the ller mixture per gallon of resinforming liquid, the penetration is increased from f gum gluten is similarly substituted, the penetra- -tion is 3.5 inches.

Omitting any one or two classes of fine particles from the filler mixture increases the depth of penetration unless particles of extreme neness (i. e., below 0.006 micron) are present. In the following Table II, is tabulated dataA showing the depth of penetration into Ottawa sand of 57 darcies permeability of ya phenolaldehyde type resin-forming liquid at C. under a pressure of -2000 p.s.i. to which liquid various amounts of filler constituents were added: Y

Table II Pounds of Filler Contsituent Per Gallon ol Resin-Forming Liquid Particle Size Range, in Mlcrons B tion-into l No' icou-wol 10o-1 1-0. 01 lo. 01-0. 006 elsdhf 1- Forming l* 111er Liquid Biotite Gum Mica Clay Clay omen Inches 2 2 l 1 0. 75 2 0 1 1 3. 00

Cascin 2 2 1 1 1. 00 1 2 1 l l. 50 2 l 1 1 2:0 6 2 2 0. 5 1 2. 0 2 2 1 0. 5 2. 0 2 0 1 1 3. 0 0 2 1 1 2. 5 2 2 2 0 4 It will be understood that in some instances, the impregnated well wall need not be perforated as when it is desired to form a complete shutoi in some zone of the well. In such instances, the treatmentmay be c'onned-as by the useV of packing devices, to the particular zone selected for treatment. In `the usual case, however, an entire section of an uncased portion of a well may be treated-usually below a packer and after removing the packer and clearing the bore, as by drilling, the impregnated well Wallis perforated at selected points as by the use of a' conventional gun perforator. The depth to which the sealing liquid is permitted to penetrate the well wall is controlled according to Whether the treated Well Wall is to be perforated. In those instances where perforation is required, it is desirable to limit the depth of penetration to between about 1 and 3 inches, Whereas where the perforation step is not required greater penetration is permissible, such as up to 6 inches.

y By the use of the particular type of fillers here set forth, it is apparent that one may regulate the depth of penetration to rwithin the required limits regardless of the permeability of the earth formations and in spite ofthe high differential pressure normally existing or., applied across the resin-forming liquid and filler mixture at the face of the well hole Wall during impregnation. The amount of resin-forming liquid to employ is calculated from the diameter of the open well hole, the depth of penetration, the porosity of the earth formation, and the length of well hole to be treated, and amounts to the volume of the accessible voids in the annular sheath formed by the impregnation, together lwith the volume of the well hole adjacent to the sheath.

The process of the invention maybe further explained by reference to the accompanying drawing. .i

In the said drawing, Fig-1 illustrates in vertical section a well bore suitably equipped vfor carrying out the impregnation step of the invention.

Fig. 2 illustrates in vertical section aportion of the impregnated well bore of Fig. 1 prepared for and undergoing gun perforation.

As shown, the upper portion of the well bore I is cased with a casing 2 andpasses through the earth formations 3 overlying the productive stratum 4. The casingv is-cemented in place with a cement 5. The top of the casing is provided with a head E through which extends a tubing string 'I carrying a packer 8 which isset in the bore so as to seal the annular space between the tubing and well bore near the top of the porl tion 9 of the well bore wall to be impregnated. Coupling means I0 permits the tubing string to be coupled or uncoupled from the packer. A back pressure valve II in the passage I2 prevents fluid below the packer from passing upwardly through the passage into the tubing string. Y

In Fig. 2, a part of the impregnated well bore 9 is shown, after removal of the packer and solidied impregnant from within the bore, with gun perforator I3 lowered on a cable I4 into position for perforating. The gun perforator is provided with a series of laterally directed barrels I5 containing a projectile I6, explosive charge I'I, and fuse (not shown), connected by fuse lead I8 to an electrical firing device (not shown) for ring the projectile through the impregnated well wall In one way of treating a well according to the invention, the tubing string 'I carrying packer 8 on its lower end is lowered into the well until the packer is near the top -of the portion 9 of the bore to be treated and then the packer is set so as to seal the annular space between the tubing and the well bore. A fluid mixture of a liquid capable sired depth of penetration into the wellv wall. As.

the uid penetrates the Well wall ller deposits `as a cake 20 and limits the penetration of the resin liquid of the iiuid mixture to the selected depth in accordance with the amount and particle f size of the ller in the uid mixture as already described.

When the wall is to be selectively perforated after treatment, sufficient filler of the specifications heretofore set forth is incorporated in the resin-forming liquid to allow a penetration of between about 1 and 3 inches while the impregnation pressure is maintained and the liquid is setting. Differential pressures of between about 1000 and 3500 pounds per square inch may be used and the depth of penetration will be substantially uniform over the entire well wall,

The back pressure valve I I prevents the resinforming liquid filler mixture from returning so that after the calculated volume has been delivered into the well hole below the valve to fill the well hole and impregnate the Well wall to the desired depth, suicient time is allowed t0 elapse for the resin-forming liquid to complete its transportation into a solid resinous mass. The time required as aforesaid varies with the temperature of the well hole, kind of resin-forming liquid used and catalyst, if any, used to promote the hardening reaction. Usually setting occurs in about 2 to 8 hours.

After the resin has hardened, the packer is unseated, if possible, and withdrawn from the well with the tubing string. If the packervcannot be unseated, the tubing string is disconnected at the coupling I0 and withdrawn from the well.` The well hole is then drilled out, if necessary, along with the packer, if not withdrawn with the tubing string, so as to clear the well hole of set resin and expose the impregnated well. This may be accomplished by using a conventional rotary or cable tool drill, thereby forming an axial hole through the treated portion of the well. A perforating tool, such as the gun perforator I3, is lowered into the well hole to the level it is desired to perfcrate and passages 2| are formed in I the impregnated well hole wall I9 by ring projectiles I6 from the gun through the impregnated wall into the surrounding formation. The perforator is then withdrawn from the well.

Other procedures for treating the earth formations with the resin-forming liquid-filler mixture may be used and will occur to those familiar with the art of well construction and remedial work. In some instances, it is preferable to place the mixture in the well by means of a dump bailer. Displacement of the mixture from the well hole into the pores of the well wall may be acc-omplished by the use of oil or water or other fluids.

As aforesaid, various resin-forming liquids may be used which spontaneously charge into hard resins under conditions of use in the well. Thermosetting resins are often used. As an example of a resin-forming liquid of the phen-olaldehyde type, the following may be cited. Mix together 390 pounds of phenol, 506 poundsof a '7 40 per cent of aqueous solution of formaldehyde, and 50 pounds of a 50 per cent aqueous solution of caustiosoda, and cookY the mixture for 21/2 hours at175 F. The cooked mixtureis-cooled and neu.- tralized. to a pH of about 4 by the addition of about6.4 gallons of a 32 per cent aqueous solution of; hydrochloric acid. This procedure prepares about 64 gallons of a resin-forming liquid which-fisready for use. It slowly hardens at ordinary temperatures. The rate of hardening increases with the temperature and at 200 F. the liquid resin becomes quite hard .in about 3 hours.

The rate of hardening may be further increased or the temperature at which hardening occurs is decreased by the addition of an alkaline catalyst,

the use of which is usually necessary to reduce the hardening time to within desirable limits'in most wells. An example of an alkaline catalyst isone prepared by dissolving 275 pounds of cal cined potassium carbonate, and 41 pounds of solid potassium hydroxide in 316 pounds of water to form a solution. This alkaline solutionmay be used with the resin-forming liquid in amounts between about 0.05 and 0.25 gallon per gallon of the. resin-forming liquid v Y, Table III sets forth examples of the use .of the resin-forming liquid just described with various amounts of the alkaline catalyst liquid, above described, in conjunction with a ller mixture comprising by weight 33.3 per cent of biotite mica `having particle sizes in the range of 1000 to 100 microns, 33.3 per cent of a clay having par. ticle s izesinthe range of, 100 to 1 microns, 16.7 percent of a clay having particle sizes in the range'of 1 to 0.01. micron, and 16.7 per cent gum gluten having particles in the range of 0.01 to 0.006 micron. The table also shows the depth of penetration into Ottawa sand having a permeability of 57 darces of the resin-forming liquid-` ller mixture at a high pressure Vdiierential. In these tests, the pressure was applied for 4 hours time-near the end of which the resin-forming liquid formed a solid mass sealing the interstices of the sand.

Table III In forming the mixtureof resin-fornling` liquid vigorous agitation or'stirring. Some time (eg.

. We claim:

.The method of controlling the depth of pene;- tration into the wall of a well holer penetrating ,an yearth formation of -a partially resinied liquid .mixture of a phenol and an aldehyde capable of` transformation into a resinous solid in situ in the earth which comprises intermi-xing with the partially resinied liquid mixture nelydivided solids; introducing the resulting mixture into the ywell hole; and applying pressure to the said rye-l sulting liquid mixturey while the partially.resinined liquid mixture forms asolid resin in situ,- said 4inely-divided solids comprising by weight 25.1130 llO-per cent of a finely-divided mineral selected from the group consisting of mica and sil-ica substantially ally of' theparticles of which have a size between about 1000 andmicrons: 25to 40 per cent of a finely-divided mineral selected from the group consisting ofiron oxide andlclaysubstantially all of the particles which have a size between about 100 to 1 microns,'12 to 20 per cent of a finely-divided mineral selected from the group consisting of' chrome yellow, chromium oxide, bariumy sulfate, clay, and magnesium silicate substantially all of the particles ofv which have a size between about 1 and 0.01 micron.. and 12 to 20 per cent'of an organic hydrophiliccolloid selected from the group consisting of casein, gelatin, gum gluten, agar agar, and isoalgin.

JAMES O. CROUCH. ORLIN W. LYONS.

REFERENCES CITED The following references are of record inthe le'of this patent:

UNITED STATES PATENTS Lerch etal. May 116, 1944 

